1. Field of the Invention
The present invention relates to a surface treatment agent for aqueous ink receiving media such as ink jet recording paper, printing sheets, coating materials and so on. More particularly, it relates to a surface treatment agent that contains a hydrophilic, carboxylic acid-containing sulfopolyester.
2. Description of the Related Arts
Hydrophilic polyesters have numerous applications. For example, they are widely used in the production of papers, textiles, and sizing agents. In addition, hydrophilic polyesters are used as dispersing agents for pigments and leveling agents for cements; also, they can be incorporated into polymeric emulsions, e.g. polyester/acrylic hybrid, to improve the adhesion and to provide the system with a pseudo-Newtonian rheology property so as to be used in ink or coatings. In addition, owing to the superior adherence to almost any kind of materials, hydrophilic polyesters are also employed as water-based adhesives or hot-melt adhesives for the surface coating of papers, films, leathers, etc. Moreover, with the sharp coloration and superior adherence, they have been used as surface treatment agents for aqueous ink printing media. In recent years, some ink jet receiving layers that contain hydrophilic polyesters have been developed.
U.S. Pat. No. 4,903,041 discloses transparent image-recording media having ink-receptive layers that contain a combination of a vinyl pyrrolidone polymer with a polyester, namely poly(cyclohexylenedimethylene-co-oxydiethylene isophthalate-co-sodio-sulfobenzenedicarboxylate), which is dispersed in the vinyl pyrrolidone to control ink dot size. Unfortunately, color images formed on the ink-receptive surface by ink jet printers are generally poor in water resistance.
U.S. Pat. No. 5,084,340 discloses transparent image-recording elements that contain ink-receptive layers that can be imaged by the application of aqueous ink dots. The ink-receptive layers contain a combination of a vinyl pyrrolidone, a polyester, a homopolymer or a copolymer of an alkylene oxide, a polyvinyl alcohol, a fluorocarbon surfactant, and inert particles, wherein said polyester is poly(cyclohexylenedimethylene-co-oxydiethylene isophthalate-co-sodio-sulfobenzenedicarboxylate). The ink-receptive layer is capable of controlling ink dot size and its surface exhibits enhanced smoothness. However, this requires a fluorocarbon surfactant and yet produced color images by ink jet printers are poor in water resistance.
Japanese Laid Open Patent Application No. 8-310,112 discloses an ink jet recording paper having, on the surface of a support, at least two ink-receptive layers comprising synthetic amorphous silica and an aqueous adhesive. The image quality and resolution are improved by adding low-molecular-weight surfactants, i.e., sulfocarboxylic acid diethylpentyl ester and sulfocarboxylic acid dimethylhexyl ester, to the base layer.
Japanese Laid Open Patent Application No. 8-310,113 discloses also an ink jet recording paper having, on the surface of a support, an ink-receptive layer comprising synthetic amorphous silica and an aqueous adhesive. The ink-receptive layer further contains a low-molecular-weight surfactant, particularly sulfocarboxylic acid di-4-methylpentyl ester, to prevent the ink staining of images.
Although the ink-receptive layers of the prior arts can provide a better image quality and higher image resolution, they have generally failed to provide sufficient adhesion. Consequently, they generally cannot be directly coated onto substrates but instead require a primer coating as help, which is inconvenient and inefficient for manufacturing. Besides, they are generally poor in water resistance, color saturation, and anti-blocking characteristics. Still another shortcoming of conventional ink receiving elements is that the produced images are prone to crack when using a pigment-based black ink to apply ink dots.